1. Field of the Invention
The present invention generally relates to computer-implemented methods for determining if actual defects are potentially systematic defects or potentially random defects. Certain embodiments relate to determining if actual defects are potentially systematic defects or potentially random defects by comparing actual defects grouped by design to randomly generated defects grouped by design.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
An integrated circuit (IC) design may be developed using a method or system such as electronic design automation (FDA), computer aided design (CAD), and other IC design software. Such methods and systems may also be used to generate a circuit pattern database from the IC design. The circuit pattern database includes data representing a plurality of layouts for various layers of the IC. Data in the circuit pattern database may, therefore, be used to determine layouts for a plurality of reticles. A layout of a reticle generally includes polygons that define features in a pattern on the reticle. Each reticle is used to fabricate one of the various layers of the IC. The layers of the IC may include, for example, a junction pattern in a semiconductor substrate, a gate dielectric pattern, a gate electrode pattern, a contact pattern in an interlevel dielectric, and an interconnect pattern on a metallization layer.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices such as ICs. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.
As design rules shrink, however, semiconductor manufacturing processes may be operating closer to the limitations on the performance capability of the processes. In addition, smaller defects can have an impact on the electrical parameters of the device as the design rules shrink, which drives more sensitive inspections. Therefore, as design rules shrink, the population of potentially yield relevant defects detected by inspection grows dramatically. As a result, more and more defects may be detected on the wafers, and correcting the processes to eliminate all of the defects may be difficult and expensive. As such, determining which of the defects actually have an effect on the electrical parameters of the devices and the yield may allow process control methods to be focused on those defects while largely ignoring others. Furthermore, at smaller design rules, process induced failures may, in some cases, tend to be systematic. That is, process induced failures tend to fail at predetermined design patterns often repeated many times within the design. In addition, although defects are generally related to process and design interaction, process induced failures are defects that are created from the artifacts of process variation not necessarily due to weak design and process variations. Systematic defects are structurally repeating defects that still may be distributed at random locations spatially. Elimination of systematic, electrically relevant defects is important because eliminating such defects can have a significant overall impact on yield.
One currently used method for separating systematic and random defects uses repeater analysis. Another method for separating systematic and random defects relies upon a user-defined horizontal cut-line (or threshold) applied to a Pareto chart illustrating defects grouped by similarity between design clips. Groups that include a number of defects higher than this cut-line are defined to be potential systematic defects although, in general, systematic defects are not identified based on defect count alone. In particular, review of potential systematic defects is generally performed. However, such methods have a number of disadvantages. For example, such previously used methods require user intervention and judgment to determine the threshold. In addition, random defect groups are known to often have higher defect counts than defect counts of systematic defect groups. As such, these previously used methods may produce incorrect results by identifying groups of random defects as potential systematic defects. In addition, the Pareto chart cut-line based methods may not be effective for determining which defect bins include potentially systematic defects since, if it is assumed that all defects on a given wafer are random defects (i.e., a 0% systematic assumption), then the defect counts shown in a Pareto chart illustrating the results of design based grouping may report only the relative area of different circuit structures on the wafer.
Accordingly, it may be advantageous to develop computer-implemented methods for determining if defects are potentially systematic defects or potentially random defects, which can be performed without user intervention and judgment and have higher accuracy than currently used methods for differentiating between potentially systematic defects and potentially random defects.